Pilot design for millimeter wave broadband

ABSTRACT

A transmitter in a wireless network configured to utilize a pilot design and channel estimation strategy to reduce pilot overhead, the pilot design based on a channel decomposition of the channel in a ray tracing channel model. A method of using a three tiered pilot design in a millimeter wave broadband (MMB) wireless network to estimate channel state information (CSI) may include assigning a first tier pilot to a first set of resource blocks, assigning a second tier pilot to second set of resource blocks, assigning a third tier pilot in a third set of resource blocks. When two of the pilots are assigned to a common resource block, the lower tier pilot may be given preference over the higher tier pilot.

CROSS-REFERENCE TO RELATED APPLICATION(S) AND CLAIM OF PRIORITY

The present application claims priority to U.S. Provisional PatentApplication Ser. No. 61/646,108 filed May 11, 2012, entitled “PilotDesign For Spatial Channel Estimation In MMB” and U.S. ProvisionalPatent Application Ser. No. 61/662,200 filed Jun. 20, 2012, entitled“Multi-Tiered CSI Pilot Design For MMB”. The content of theabove-identified patent documents is incorporated herein by reference.

TECHNICAL FIELD

The present application relates generally to telephonic communicationsand, more specifically, to a signaling system for a millimeter wavebroadband (MMB).

BACKGROUND

In current cellular systems, a strategy to estimate the channel may beto transmit n_(T) pilots (one for each antenna) on orthogonal signals(whether frequency or code). Each such signal may be received at allreceive (Rx) antennas and then separated so that the channel from eachtransmit (Tx) to each Rx can be independently estimated. In addition thepilots may be repeated in frequency, because the channel may befrequency selective.

SUMMARY

Embodiments disclosed herein relate to a transmitter in a wirelessnetwork configured to utilize a pilot design and channel estimationstrategy to reduce pilot overhead, the pilot design based on a channeldecomposition of the channel in a ray tracing channel model.

Embodiments disclosed herein relate to a wireless network configured totransmit pilot signals in a resource block using a plurality ofantennas, wherein the number of pilot signals in a resource block isless than the number of antennas used to transmit the pilot signals inthe resource block.

Embodiments disclosed herein relate to a method of using a three tieredpilot design in a millimeter wave broadband (MMB) wireless network toestimate channel state information (CSI). The method may includeassigning a first tier pilot to a first set of resource blocks,assigning a second tier pilot to second set of resource blocks,assigning a third tier pilot in a third set of resource blocks, whereinwhen two of the pilots are assigned to a common resource block, thelower tier pilot is given preference over the higher tier pilot. Themethod may also include transmitting each of the first tier pilot, thesecond tier pilot, and the third tier pilot to a user equipment.

Embodiments disclosed herein relate to a method of establishing a pilotstructure between a base station and a UE. The method may includebroadcasting from the base station information relating to the pilotstructure, receiving the information at the user equipment, determiningthe pilot structure with the information broadcast from the basestation, and returning CSI values from the user equipment to the basestation.

Before undertaking the DETAILED DESCRIPTION below, it may beadvantageous to set forth definitions of certain words and phrases usedthroughout this patent document: the terms “include” and “comprise,” aswell as derivatives thereof, mean inclusion without limitation; the term“or,” is inclusive, meaning and/or; the phrases “associated with” and“associated therewith,” as well as derivatives thereof, may mean toinclude, be included within, interconnect with, contain, be containedwithin, connect to or with, couple to or with, be communicable with,cooperate with, interleave, juxtapose, be proximate to, be bound to orwith, have, have a property of, or the like; and the term “controller”means any device, system or part thereof that controls at least oneoperation, such a device may be implemented in hardware, firmware orsoftware, or some combination of at least two of the same. It should benoted that the functionality associated with any particular controllermay be centralized or distributed, whether locally or remotely.Definitions for certain words and phrases are provided throughout thispatent document, those of ordinary skill in the art should understandthat in many, if not most instances, such definitions apply to prior, aswell as future uses of such defined words and phrases.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present disclosure and itsadvantages, reference is now made to the following description taken inconjunction with the accompanying drawings, in which like referencenumerals represent like parts:

FIG. 1 illustrates a ray tracing channel model according to embodimentsof the present disclosure;

FIG. 2 illustrates an architecture for millimeter wave broadband (MMB)according to embodiments of the present disclosure;

FIG. 3 illustrates an angle of arrival/angle of departure (AOA/AOD)estimation pilot illustration of (k, l, m) according to embodiments ofthe present disclosure;

FIG. 4 illustrates an AOA/AOD estimation pilot according to embodimentsof the present disclosure;

FIG. 5 illustrates a flow chart of a base station and user equipmentprocedure for determining CSI values in MMB according to embodiments ofthe present disclosure;

FIG. 6 illustrates a flow chart of a base station and user equipmentprocedure for determining CSI values in MMB according to embodiments ofthe present disclosure;

FIG. 7 illustrates a flow chart of a base station and user equipmentprocedure for determining CSI values in MMB according to embodiments ofthe present disclosure;

FIG. 8 illustrates a flow chart of a base station and user equipmentprocedure for determining CSI values in MMB according to embodiments ofthe present disclosure;

FIG. 9 illustrates an AOD with user location according to an exemplaryembodiment of the disclosure;

FIG. 10 illustrates a three tiered pilot structure for MMB according toembodiments of the present disclosure;

FIG. 11 illustrates a specific example of a three tiered pilot accordingto embodiments of the present disclosure;

FIG. 12 illustrates a flow chart of a base station and user equipmentprocedure for determining CSI values in MMB according to embodiments ofthe present disclosure

FIG. 13 illustrates a flow chart of a base station and user equipmentprocedure for determining CSI values in MMB according to embodiments ofthe present disclosure; and

FIG. 14 illustrates a flow chart of a base station and user equipmentprocedure for determining CSI values in MMB according to embodiments ofthe present disclosure;

FIG. 15 illustrates a wireless network according to an embodiment of thepresent disclosure;

FIG. 16A illustrates a high-level diagram of a wireless transmit pathaccording to an embodiment of this disclosure;

FIG. 16B illustrates a high-level diagram of a wireless receive pathaccording to an embodiment of this disclosure; and

FIG. 17 illustrates a subscriber station according to an exemplaryembodiment of the disclosure

DETAILED DESCRIPTION

FIGS. 1 through 17, discussed below, and the various embodiments used todescribe the principles of the present disclosure in this patentdocument are by way of illustration only and should not be construed inany way to limit the scope of the disclosure. Those skilled in the artwill understand that the principles of the present disclosure may beimplemented in any suitably arranged telecommunications system.

The following three documents and standards descriptions are herebyincorporated into the present disclosure as if fully set forth herein:

Reference 1 (REF1): 3GPP TS 36.211 LTE Physical channels and modulation,v. 10;

Reference 2 (REF2): “Millimeter wave propagation: Spectrum managementimplications”, Federal Communications Commission, Office of Engineeringand Technology, Bulletin Number 70, July, 1997; and

Reference 3 (REF3): Zhouyue Pi, Farooq Khan, “An introduction tomillimeter-wave mobile broadband systems”, IEEE Communications Magazine,June 2011.

FIG. 1 illustrates a ray tracing channel model according to embodimentsof the present disclosure. The embodiment of the ray tracing channelmodel shown in FIG. 1 is for illustration only. Other embodiments couldbe used without departing from the scope of this disclosure.

A cellular system 100 includes n_(T) transmit antennas 110, n_(R)receive antennas 112 and p paths 114. In current cellular systems(REF1), a strategy to estimate the channel may be to transmit n_(T)pilots (one for each antenna) on orthogonal signals (whether frequencyor code). Each such signal may be received at all Rx antennas 110, andthen separated so that the channel from each Tx to each Rx can beindependently estimated. In addition the pilots may be repeated infrequency, because the channel may be frequency selective. For largenumber of antennas at the base station and mobile station, the problemof channel estimation and feedback may be magnified.

Due to a lack of available spectrum in the low frequencies one optionmay be to use frequencies that are an order of magnitude higher thancurrent cellular frequencies as proposed in millimeter wave broadband(REF2, and REF3). For electromagnetic radiation the path loss isinversely proportional to the square of the frequency. To make MMBfeasible this path loss may be countered by using very large arrays ofantennas at the receiver and transmitter in order to achieve beamforminggain.

FIG. 2 illustrates an architecture for millimeter wave broadband (MMB)according to embodiments of the present disclosure. The embodiment ofthe MMB architecture shown in FIG. 2 is for illustration only. Otherembodiments could be used without departing from the scope of thisdisclosure.

Driving large antenna arrays by using a separate baseband chain for eachantenna may be complex and expensive. An architecture in MMB isillustrated in FIG. 2. This MMB architecture 200 may use low cost analogphase shifters 210 in front of each antenna 212, and multiple antennas212 may be fed signal from only one digital (baseband) chain 214. Weassume that we have K_(T), K_(R) digital chains 214 at the receiver 216and transmitter 218 respectively. Each of the chains 214 at thetransmitter 218 is connected to NTRF antennas 212 and the receiver isconnected to NRRF antennas 212.

For a system like the one illustrated in FIG. 2, there may be at leasttwo issues with the commonly used strategy for pilot transmission. Oneis that there is a humongous number of antennas 212. Therefore,transmission of n_(T) pilots per RB is a lot of overhead. Assume that wehave the same number of REs per RB as in LTE. Then if we have 128antennas at the transmitter, then we need to have 128 pilots per RB,while REs per RBs is 144. Such an approach will use almost all of theresources for pilot transmission and hence is clearly infeasible.

Another issue is that the MMB architecture 200 shown in FIG. 2 in whichmultiple antennas 212 are driven by one digital chain 214 restricts ourfreedom to transmit orthogonal signals in frequency. A differentapproach than the one currently used is therefore necessary.

An alternative pilot design and channel estimation strategy maysubstantially reduce the pilot overhead. This pilot design is based onthe channel decomposition of the channel in FIG. 1 as shown in Equation1a:

$\begin{matrix}{H = {{\begin{bmatrix}1 & 1 & \ldots & 1 \\^{j\; \theta_{1}} & ^{j\; \theta_{2}} & \ldots & ^{j\; \theta_{p}} \\\vdots & \vdots & \vdots & \vdots \\^{{({n_{R} - 1})}j\; \theta_{1}} & ^{{({n_{R} - 1})}j\; \theta_{2}} & \ldots & ^{{({n_{R} - 1})}j\; \theta_{P}}\end{bmatrix}\begin{bmatrix}h_{1} & 0 & \ldots & 0 \\0 & h_{2} & \ldots & 0 \\\vdots & \vdots & \vdots & \vdots \\0 & 0 & \ldots & h_{p}\end{bmatrix}}{\quad\begin{bmatrix}1 & ^{j\; \theta_{1}} & \ldots & ^{{({n_{t} - 1})}j\; \theta_{1}} \\1 & ^{j\; \theta_{2}} & \ldots & ^{{({n_{t} - 1})}j\; \theta_{2}} \\\vdots & \vdots & \vdots & \vdots \\1 & ^{j\; \theta_{p}} & \ldots & ^{{({n_{t} - 1})}j\; \theta_{p}}\end{bmatrix}}}} & \left( {1a} \right)\end{matrix}$

In this representation of the channel, the number of variables is equalto 3p, as opposed to n_(R)×n_(T). If the number of paths is much lessthan n_(T)×n_(R) then it is advantageous to send a pilot signal enoughtimes to estimate the 3p parameters as opposed to estimating the fulln_(R)×n_(T) components of the H matrix individually.

In general, even a non MMB system using a pilot design in which theoverhead scales as n_(T) may be problematic because with increase in thenumber of antennas, there may be not only the power gain frombeamforming (and capacity gain from SDMA) but also the loss incurredfrom pilot overhead. At some point these two may cancel each other out,putting a limit on the number of antennas that can be used and themaximum gains that can be realized. However, if we were to characterizethe channel in terms of the number of paths, then the beamforming andSDMA gains could be potentially unbounded by increasing the number of Txantennas.

Observing the spatial channel model it is clear that a small number ofvariables (3p) may fully determine the system, even if we keep on addingnew antennas at the base station and the mobile station. Therefore thepilot overhead may not scale with the number of antennas at the BS andMS for any communication system, but should be limited by the number ofpaths. In other words, even if current designs may be based on separatepilots for each transmit antennas, in MMB systems with the use of largenumber of antennas to increase channel capacity, even at lowerfrequencies, pilots may have to be designed to be limited by the numberof paths and not scale with the number of Tx antennas.

In certain embodiments of this disclosure, a pilot is designed toestimate the spatial characteristic of the channel viz. the angles ofarrival and the angles of departures for each path from the BS to UE.Being spatial characteristics angle of arrivals and departures may beinvariant across frequency. Therefore the spatial pilot may not requirefrequent repetition across frequency.

It can be assumed that an upper bound on P on the number of paths p isknown. This upper bound is cell specific. A rural cell may have P=2,while an urban cell may have P as large as 10.

The received signal may be given as according to Equation 1b.

y=F _(RRF) HF _(TRF) s+n  (1b)

Where F_(RRF), F_(TRF) are block diagonal matrices, where each block ofF_(RRF) is of size 1×N_(RRF), and the i^(th) block consists of thephases used in the i^(th) digital chain 214 in FIG. 2. Similarly eachblock of F_(TRF) is of size N_(TRF)×1 and the i^(th) block mayessentially consist of the phases used in the i^(th) digital chain 214in FIG. 2. As discussed before the number of independent variables thatdetermine H may be at most 3P.

To estimate AOA and AOD, 3P parameters may need to be extracted, as mayfollow from the observation in Equation 1b. To estimate 3P parameters wemay need 3P equations. However the number of equations in Equation 1b isequal to K_(R). Embodiments of the present disclosure describe how thepilot is transmitted to augment the equations to be greater than orequal to 3P. In contrast to traditional pilot design schemes, thisscheme also may require varying the receive and transmit precoders toachieve the desired number of equations for the 3P variables.

In the procedure below, the number of independent equations can besuccessively augmented. In each of the augmentation steps, anobservation of the form LHR is obtained. For example initially inEquation 1b L=F_(RRF), and R=F_(TRF)×s. The number of equations in suchan observation is equal to rows(L)×Cols(R), assuming L and R are fullrank. If L or R are not full rank then the number of equations isreduced, for example if some of the rows of L are linear combinations ofothers, then the equations corresponding to these rows are linearcombination of the equations corresponding to other rows and hence notindependent, thus it may be desirable to augment the number of equationsin a manner so that L and R are full rank.

The pilot design may follow three stages which are explained below:

Stage I: Vary pilot across frequency

In certain embodiments, the transmitter transmits pilots [s₁, . . . ,s_(k)]. Here, the input output representation becomes:

[y ₁ , . . . , y _(k) ]=F _(RRF) HF _(TRF) [s ₁ , . . . , s _(k) ]+[n ₁, . . . , n _(k)]  (1c)

This step augments the number of equation to K_(R)×k.

In one embodiment the transmitter transmits pilots [s₁, . . . , s_(K)_(T) ], which are orthogonal. Here, the input output representationbecomes.

[y ₁ , . . . , y _(K) _(T) ]=F _(RRF) HF _(TRF) [s ₁ , . . . , s _(K)_(T) ]+[n ₁ , . . . , n _(K) _(T])   (1d)

Let S=[s₁, . . . , s_(K) _(T) ], by post-multiplying both sides withS^(H), the equation may be represented as shown in Equation 2:

[y ₁ , . . . , y _(K) _(T) ][s ₁ , . . . , s _(K) _(T) ]^(H) =F _(RRF)HF _(TRF) +[n′ ₁ , . . . , n′ _(K) _(T])   (2)

Here, Y_(I)=[y₁, . . . , y_(K) _(T) ][s₁, . . . , s_(K) _(T) ]^(H),where I stands for the first stage. The orthonormal choice of [s₁, . . ., s_(K) _(T) ] ensures that the noise is still i.i.d. This choice ofpilot thus ensures that we have an observation of the form Equation 2irrespective of the pilot choice (for example if the pilot hops acrossdifferent values). This ensures a consistent detection problem at the UEand simplifies its receiver algorithm and implementation.

Stage II: Repeat Stage I in time: (fixed F_(TRF) varying F_(RRF)). Thesecond augmentation step is to increase the number of rows in L asdiscussed above. In the second stage, F_(TRF) is maintained as fixed andF_(RRF) is varied l times in time, with which the stacked equation 3 isobtained:

$\begin{matrix}{\begin{bmatrix}{Y_{I}(1)} \\\vdots \\{Y_{I}(l)}\end{bmatrix} = {{\begin{bmatrix}F_{{RRF}{(1)}} \\\vdots \\F_{{RRF}{(l)}}\end{bmatrix}{HF}_{TRF}} + \begin{bmatrix}{N_{I}(1)} \\\vdots \\{N_{I}(l)}\end{bmatrix}}} & (3)\end{matrix}$

Note that in the second stage the only base station procedure is to keepF_(TRF) fixed. It is up to the receiver to vary F_(RRF) to be able toaugment the number of rows in the L matrix. Further note that the rowsof Equation 3 can be permuted in a manner so that the first row of thematrices F_(RRF)(i) are together, then the second rows are together, andso on. This can be achieved by multiplying both sides by a squarepermutation matrix P₁. Which does not have any effect on the statisticalproperties of the noise. However the resulting matrix:

$\begin{matrix}{{F_{P} = {P\begin{bmatrix}F_{{RRF}{(1)}} \\\vdots \\F_{{RRF}{(l)}}\end{bmatrix}}},} & (4)\end{matrix}$

is block diagonal, with each block of size l×NRRF. Further the receivercan choose F_(RRF), in such a fashion that the, rows are linearlyindependent for each block diagonal matrix, or equivalently each blockdiagonal element is full rank. Any choice of linearly independent rowsmay be used.

In certain embodiments, a fixed set of orthogonal rows is used by the UEfor the F_(RRF) components in F_(p). In one embodiment the UE hopsacross various choice of F_(RRF).

Stage III: Repeat Stage II in time: vary F_(TRF): the pilot is repeatedin stage I and II, for various F_(TRF). After stage II the number ofequation is equal to l×k×K_(R). F_(TRF) is varied so as to make thetotal number of equations equal to 3P. Therefore an additionalrepetition of

$\frac{3P}{l \times K_{R} \times k}$

is required. In general, the number of times Stage III is repeated isdenoted as m. Repeating steps I and II for m values of F_(TRF), theobservations as can be written as:

[Y _(II)(1), . . . , Y _(II(m)) ]=F _(p) H[F _(TRF)(1), . . . , F_(TRF)(m)]+[N ₁ , . . . , N _(m)]  (5)

As before a permutation matrix post-multiplying both sides will permutethe columns of F=[F_(TRF)(1), . . . , F_(TRF)(m)], so that it becomesblock diagonal. It is a sensible choice choose the columns such thatthey are linearly independent, otherwise some of the columns of F arelinear combination of others and thus redundant.

In certain embodiments, a fixed set of orthogonal columns is used by theBS for the component in F_(TRF)(i). In one embodiment, the BS hopsacross various choice of F_(TRF).

Finally the number of pilots are given as follows:

Pilots in Frequency: k; Pilots in Time: 1×m; and

Total Pilots overhead: (k×1×m).

To recover 3P variables the pilot overhead is equal to

$\frac{3P}{K_{R}}.$

Note that this pilot overhead is for all of the subbands. Since AOA/AODis a spatial characteristic it remains unchanged over the entiresubband, and this pilot could be transmitted in the center RE, orrepeated sparsely over the frequency if so desired. Thus the pilotoverhead over a large band is vanishingly small.

FIG. 3 illustrates an angle of arrival/angle of departure (AOA/AOD)estimation pilot illustration of (k, l, m) according to embodiments ofthe present disclosure.

FIG. 4 illustrates an AOA/AOD estimation pilot according to embodimentsof the present disclosure. The embodiments of the AOA/AOD estimationshown in FIGS. 3 and 4 are for illustration only. Other embodimentscould be used without departing from the scope of this disclosure.

Below is described an example of the design disclosed above. Thisexample pilot design is shown in FIG. 3, and shown in more detail inFIG. 4. Many alternatives are possible, and this example is chosen amongthe many alternatives merely to serve as a illustrative example, andshould not be construed as limiting or preferred over other examples.Assume there is an 8 Tx, 4 Rx system with 2 Rf chains at the transmitterand one at the receiver, and an upper bound on the number of paths equalto 4.

Stage I: Since K_(T) 310 is equal to 2 we send two pilots in frequency312.

Stage II: We choose l=2, note that this is minimum required to preservethe AOA information. “1×m” 314 is shown in FIG. 3 along the time axis316.

Stage III: m=3 is chosen to ensure that k×l×m×K_(R) is greater than 3Por 12 as shown in the shaded region 318 in FIG. 3. In the example shownin FIG. 4, 12 pilots 140 with are shown with the enumeration of each ofthe indices.

Several other embodiments based upon the pilot design proposed hereinare as follows.

FIG. 5 illustrates a flow chart of a base station and user equipmentprocedure for determining CSI values in MMB according to embodiments ofthe present disclosure. The embodiment of the process shown in FIG. 5 isfor illustration only. While the flow chart depicts a series ofsequential steps, unless explicitly stated, no inference should be drawnfrom that sequence regarding specific order of performance, performanceof steps or portions thereof serially rather than concurrently or in anoverlapping manner, or performance of the steps depicted exclusivelywithout the occurrence of intervening or intermediate steps. The processdepicted in the example depicted is implemented by a transmitter chainin, for example, a mobile station.

In some embodiments, the values k, l and m or the number of repetitionsof the three stages are cell specific in a particular cell and can beconveyed to the UEs in a broadcast message at 510. The broadcast messagecan be transmitted for example through the PBCH or PDCCH. This procedureis illustrated in FIG. 5.

FIG. 6 illustrates a flow chart of a base station and user equipmentprocedure for determining CSI values in MMB according to embodiments ofthe present disclosure. The embodiment of the process shown in FIG. 6 isfor illustration only. While the flow chart depicts a series ofsequential steps, unless explicitly stated, no inference should be drawnfrom that sequence regarding specific order of performance, performanceof steps or portions thereof serially rather than concurrently or in anoverlapping manner, or performance of the steps depicted exclusivelywithout the occurrence of intervening or intermediate steps. The processdepicted in the example depicted is implemented by a transmitter chainin, for example, a mobile station.

In some embodiments, the values of (k, l, m) can be implicitly describedby a single number P (which can be the proxy for number of paths in asystem), as in the example given above. The base station can broadcastthis value at 610 to all the UEs. The UEs then decode the values of k, land m at 620. Thereafter, the UEs proceed to decode the pilot and reportback CSI at 630.

In some embodiments, the values of F_(RRF)(i) and F_(TRF)(j) can bepre-specified, such as stored in a memory, and must be adhered to by theUE and base station. The UE can signal the values of k, l, and m by thebase station. The UE then knows the pilot structure. It also knows thevalue of F_(TRF)(i) iε{1, . . . m} and F_(RRF)(i) Iε{1, . . . , l}. Bothof these values could be base station or UE specific.

In some embodiments, the values of F_(RRF)(i) may depend upon the UE id,and the Cell id. The values are cycled through based on a hoppingpattern. This is to ensure that no particular spatial configurationalways elicits a worst case performance in a given UE. In other words,the hopping pattern ensures that the worst case performance getsamortized over all the UEs. In some embodiments, the values ofF_(TRF)(i) depends upon the Cell id and cycle on a hopping pattern. Thisis to again ensure that no particular spatial configuration elicits aworst case performance in the cell.

In some embodiments, the AOA/AOD pilot location is spread out across thefrequency band at uniform intervals; the repetition of the pilot infrequency is specified by an additional parameter r broadcast by thebase station.

FIG. 7 illustrates a flow chart of a base station and user equipmentprocedure for determining CSI values in MMB according to embodiments ofthe present disclosure. The embodiment of the process shown in FIG. 7 isfor illustration only. While the flow chart depicts a series ofsequential steps, unless explicitly stated, no inference should be drawnfrom that sequence regarding specific order of performance, performanceof steps or portions thereof serially rather than concurrently or in anoverlapping manner, or performance of the steps depicted exclusivelywithout the occurrence of intervening or intermediate steps. The processdepicted in the example depicted is implemented by a transmitter chainin, for example, a mobile station.

In some embodiments, the UE uses previously detected AOA and AOD's at710 in conjunction with the current AOA and AOD at 720. The UE thencombines them with an appropriate function at 730. The UE calculates thecurrent AOA/AOD at 740. This approach reduces the noise by taking intoaccount the fact that AOA and AOD are slow changing characteristics ofthe channel. An example of this could be:

θ_(i)(t)=(1−α)θ_(i)(t−1)+α{circumflex over (θ)}_(i)  (6)

Where {circumflex over (θ)}_(i) is the currently detected AOA (or AOD)and θ_(i)(t) is the estimate AOA (or AOD) at time t.

FIG. 8 illustrates a flow chart of a base station and user equipmentprocedure for determining CSI values in MMB according to embodiments ofthe present disclosure. The embodiment of the process shown in FIG. 8 isfor illustration only. While the flow chart depicts a series ofsequential steps, unless explicitly stated, no inference should be drawnfrom that sequence regarding specific order of performance, performanceof steps or portions thereof serially rather than concurrently or in anoverlapping manner, or performance of the steps depicted exclusivelywithout the occurrence of intervening or intermediate steps. The processdepicted in the example depicted is implemented by a transmitter chainin, for example, a mobile station.

In some embodiments, the base station does not need to use all K_(T) ofits digital chains to transmit the pilot. In fact it a RF chain is usedfor pilot then it fixes the RF beamforming weights for that OFDM symbol.Hence the base station can select to use only K_(T)′<K_(T) RF chains forpilot transmission. The parameter K_(T)′ can be implicitly factored inthe pilot design and placement, for example F_(TRF) could be selectedfrom a table that varies with the number of RF chains used for pilottransmission. Referring to FIG. 8, the base station broadcasts number ofRF chains used for pilot (K_(T)′) at 810. The UE uses the values of(K_(T)′) to deduce pilot structure and base station precoder hoppingpattern. At 830, the UE feeds back CSI values to the base station. Insome embodiments, the base station uses the RF beamforming weights inaccordance with a priori knowledge about the paths in the system. Forexample, the base station can know that there are strong reflectorsbetween a pair of angles. Then the BS chooses the RF beamforming weightsso that the paths between these two angles are strengthened. The basestation coveys the values of F_(TRF) it proposes to use to the UEs in abroadcast message, possibly on the data channel.

In some embodiments, the base station choose F_(TRF) and F_(RRF) suchthat the matrix LA(θ)ΓB(□)R always has a simple structure. As describedearlier the matrices L and R are block diagonal. Suppose we chooseF_(TRF) and F_(RRF) in such a manner that the block diagonal elementsare the same. These block diagonal elements are of size NTRF×m andNRRF×l respectively, suppose l and m are chosen such that NTRF=m×a andNRRF=l×b, where a and b are integers. Then block diagonal elements in Lare such that there are l orthogonal columns which then repeat for b,times and similarly the block diagonal elements of R are such that thereare m orthogonal rows which then repeat a times. The observation isgiven as:

y=LAΓBR+N  (7)

If F₁ is denoted as the set of unique columns in L, and F₂ as the set ofunique rows in R. Then postmultiplying (4) by F₂ ^(H) and premultiplyingby F₁ ^(H), Equation 8 is obtained:

y′=A′Γ′B′+N′  (8)

Where A′ has the same structure as A albeit with reduced rows (

$\frac{n_{R}}{b}$

instead of n_(R)), Similarly B has same structure as B′ albeit withreduced rows (

$\frac{n_{T}}{a}$

instead of n_(T)). Similar Γ′ is a p×p diagonal matrix.

This method of pilot design ensures that a single algorithm for AOA/AODdetection (parameterized by l and m) can be implemented and used in themobile station, instead of having to solve a new problem that dependsupon L and R.

For MMB communications spatial channel estimation is of key importanceto enable SDMA, beamforming etc. Conventional pilot design (as in LTE)is infeasible and wasteful for large number of antennas. The proposedpilot structure incurs minimal overhead while being able to estimate thekey components of the channel. In some embodiments, a multi-tieredapproach may be taken. The channel matrix can be decomposed in asfollows:

H=A(θ₁, . . . , θ_(p))Γ(h ₁ , . . . , h _(p))B(φ₁, . . . , φ_(p),  (9)

where A(θ₁, . . . , θ_(p)) and B(φ₁, . . . , φ_(p)) are spatialcharacteristics and hence invariant across frequency. The only frequencyvarying component in the channel is the matrix Γ(h₁, . . . , h_(p)).

FIG. 9 illustrates an AOD with user location according to embodiment ofthe disclosure. The embodiments of the AOD with user location shown inFIG. 9 is for illustration only. Other embodiments could be used withoutdeparting from the scope of this disclosure.

The three components A, B and Γ have different rate of change bothacross frequency and time. A and B are spatial characteristics and henceconstant across frequency. While Γ is frequency dependent. In time theangles of arrival (A) can change much faster than the angles ofdeparture (B). This is because the angles of departures that reach acertain UE in a certain position only change when the UE positionchanges by a large amount. This is illustrated in FIG. 9, which shows anumber of users 910 near a base station 912 with several reflectors invarious paths 916. When the distances between the base station 912 andthe UEs are large, the AOD remain the same. However the AOA can changewhen the user rotates, which could be much faster than the change ofAOD. However the reflection coefficients h_(i) can change even if theuser moves by half a wavelength and thus they are the fastest changingof all.

In some embodiments, a three tiered pilot design approach may be used toestimate the CSI, based on these three components A, B and Γ. The firsttier pilot is meant to estimate all three together and thus requiresmany resources (i.e. it must contain enough redundancy to estimate 3pvariables). The second tier pilot assumes that AODs are known and onlyseeks to estimate A and Γ (thus it needs sufficient redundancy toestimate 2p variables). The third tier pilot assumes knowledge of both Aand B and just seeks to estimate Γ (Thus it requires to just estimate pvariables).

These three tiers of pilots may also differ in how frequently they mustbe repeated. For example the first tier pilot may need to be much lessfrequent than the second tier pilot which in turn must be less frequentthan the third tier pilot. Also note that only the component Γ variesacross frequency, while A and B being spatial characteristics are moreor less constant across frequency. Therefore the first and second tierpilots only need very sparse repetition (if at all across) frequency,while the third tier pilot must be repeated frequently across frequency.

For ease of notation we will henceforth refer to these three tiers ofpilots as follows:

Tier I Pilot=AOD pilot.

Tier II Pilot=AOA pilot

Tier III Pilot=CSI Pilot.

Note that the nomenclature indicates what the principal function of thepilot is. Thus the tier I pilot may not only yield AODs, it also yieldsAOAs and per path CQI as well. However, its main purpose is to get theAODs and hence it is termed the AOD pilot.

The received signal for each RE may be represented as in Equation 3A asfollows.

y=F _(RRF) HF _(TRF) s+n  (3A)

Each of these pilots may need to be constructed in a manner in space andtime so that the desired number of parameters can be extracted fromEquation 3A. The following procedure describes a way to augment thenumber of equations so that any desired M variables can be estimated.Given an upper bound on the number of paths P, the value of M for theAOD, AOA and CSI pilot may be set equal to 3P, 2P and P respectively.

Pilot Structure based on the number of variables M to be estimated:

The received signal can be given in Equation 3A above. Where F_(RRF),F_(TRF) are block diagonal matrices, where each block of F_(RRF) is ofsize 1×N_(RRF), and the i^(th) block consists of the phases used in thei^(th) digital chain in FIG. 2. Similarly each block of F_(TRF) is ofsize N_(TRF)×1 and the i^(th) block essentially consists of the phasesused in the i^(th) digital chain in FIG. 2. At most M equations need tobe extracted out of Equation 3A.

Below is an explanation of another exemplary embodiment.

To estimate M variables M equations need to be created from theobservation in Equation 9. However, the number of equations in Equation9 is equal to K_(R). The pilot is transmitted to augment the equationsto be greater than or equal to M. In contrast to traditional pilotdesign schemes, this scheme also requires varying the receive andtransmit precoders to achieve the desired number of equations for the Mvariables.

In the procedure below the number of independent equations can besuccessively augmented. In each of the augmentation steps, anobservation of the form LHR is obtained. For example initially inEquation 9 L=F_(RRF), and R=F_(TRF)×s. The number of equations in suchan observation may be equal to rows(L)×Cols(R), assuming L and R arefull rank. If L or R are not full rank then the number of equations maybe reduced, for example if some of the rows of L are linear combinationsof others, then the equations corresponding to these rows are linearcombination of the equations corresponding to other rows and hence notindependent, thus it is desirable to augment the number of equations ina manner so that L and R are full rank.

The pilot design follows three stages which are explained below:

Stage I: Vary pilot across frequency

The transmitter may transmit pilots [s₁, . . . , s_(k)]. With this theinput output representation may be represented as:

[y ₁ , . . . , y _(k) ]=F _(RRF) HF _(TRF) [s ₁ , . . . , s _(k) ]+[n ₁, . . . , n _(k)]

This step augments the number of equation to K_(R)×k.

Stage II: Repeat Stage I in time: (fixed F_(TRF) varying F_(RRF)). Thesecond augmentation step may increase the number of rows in L asdiscussed above. In the second stage, F_(TRF) can remain fixed andF_(RRF) can vary l times in time, with which the stacked equation 10 isobtained:

$\begin{matrix}{\begin{bmatrix}{Y_{I}(1)} \\\vdots \\{Y_{I}(l)}\end{bmatrix} = {{\begin{bmatrix}F_{{RRF}{(1)}} \\\vdots \\F_{{RRF}{(l)}}\end{bmatrix}{{HF}_{TRF}\left\lbrack {s_{1},\ldots \mspace{14mu},s_{k}} \right\rbrack}} + \begin{bmatrix}{N_{I}(1)} \\\vdots \\{N_{I}(l)}\end{bmatrix}}} & (10)\end{matrix}$

Note that in the second stage the only base station procedure is to keepF_(TRF) fixed. It is up to the receiver to vary F_(RRF) to be able toaugment the number of rows in the L matrix.

Stage III: Repeat Stage II in time: vary F_(TRF): the pilot in stage Iand II may be repeated for various F_(TRF). After stage II the number ofequation is equal to l×k×K_(R). We now vary F_(TRF), so as to make thetotal number of equations equal to 3P. Therefore an additionalrepetition of at least

$\frac{3P}{l \times K_{R} \times k}$

is required. In general we denote the number of times Stage III isrepeated as m. Repeating steps I and II for m values of F_(TRF) theobservations can be written as Equation 11:

$\begin{matrix}{\left. {\left\lbrack {{Y_{II}(1)},\ldots \mspace{14mu},Y_{{II}{(m)}}} \right\rbrack = {\begin{bmatrix}F_{{RRF}{(1)}} \\\vdots \\F_{{RRF}{(l)}}\end{bmatrix}{H\left\lbrack {{{F_{TRF}(1)}\left\lbrack {s_{1},\ldots \mspace{14mu},s_{k}} \right\rbrack},\ldots \mspace{14mu},}\quad \right.}{{F_{TRF}(m)}\left\lbrack {s_{1},\ldots \mspace{14mu},s_{k}} \right\rbrack}}} \right\rbrack + \left\lbrack {N_{1},\ldots \mspace{14mu},N_{m}} \right\rbrack} & (11)\end{matrix}$

As before, a permutation matrix post-multiplying both sides will permutethe columns of F=[F_(TRF)(1), . . . , F_(TRF)(m)], so that it becomesblock diagonal. It may be sensible to choose the columns such that theyare linearly independent, otherwise some of the columns of F are linearcombination of others and thus redundant.

Finally the number of pilots are given as follows:

Pilots in Frequency: k

Pilots in Time: l×m

Total Pilots overhead: (k×l×m).

To recover M variables the pilot overhead is equal to

$\frac{M}{K_{R}}.$

Returning to the three tier design, the pilot structure of each tier isspecified by the six numbers (f, t, b, k, l, m).

Where f and t are the periodicity in frequency and time respectively,while b is location of the first RE of the pilot. The parameter k, l andm determine how many symbols of the pilot are present.

FIG. 10 illustrates a three tiered pilot structure for MMB according toembodiments of the present disclosure. The embodiment of the threetiered pilot structure for MMB shown in FIG. 10 is for illustrationonly. Other embodiments could be used without departing from the scopeof this disclosure.

FIG. 10 illustrates the three tiered design and also illustrates thatthe AOD pilot 1010 has the most number of resources, but is the sparsestin terms of repetitions within resource blocks 1040, while the CQI pilot1030 may be the most frequently repeated but it has the least number ofresources allocated for each individual instance. The AOA pilot 1020 isa tier two pilot and falls between the AOA pilot 1010 and CQI pilot1030.

FIG. 11 illustrates a specific example of a three tiered pilot accordingto embodiments of the present disclosure. The embodiment of the threetiered pilot shown in FIG. 11 is for illustration only. Otherembodiments could be used without departing from the scope of thisdisclosure.

Below is described an example of the design disclosed above. Thisexample pilot design is shown in FIG. 10, and shown in more detail inFIG. 11. Many alternatives are possible, and this example is chosenamong the many alternatives merely to serve as an illustrative example,and should not be construed as limiting or preferred over otherexamples.

Assume we have 8Tx, 4Rx system 2 Rf chains at the transmitter and one atthe receiver, and an upper bound on the number of paths equal to 4.

AOD pilot 1110

In this case 3P/K_(R)=12 We choose k=2, l=2 and m=3.

AOA pilot 1120

We have 2P/K_(R)=8. We choose k=2, l=2 and m=2.

CQI Pilot 1130

Since P/K_(R)=4. We choose k=2, l=2, m=1.

Note that the RF precoders can be chosen to align in time. This may benecessary if the same antennas are used for multiple pilots, since theRF beamforming weights are fixed for the whole OFDM symbol. Note thatFIG. 11 just shows one instance of each pilot, further the pilots areput together for ease of visualization. In general the CQI pilot will befrequent across the band, and in one RB only one of these pilots will bepresent (as in FIG. 10).

In some embodiments, when two pilots collide in the same time frequencyresource, the lower tier pilot may be placed in favor of the higher tierone. This does not cause any problems in channel estimation because theAOD pilot contains sufficient information to give us both AOA and theCQI per path. Similarly the AOA pilot contains enough data to bothdecode the AOA as well as the CQI per path. Thus it may be a sensibleapproach to puncture a lower tier pilot in favor of a higher tier one.This is also illustrated in FIG. 10, wherein the CQI pilot 130 ispunctured in favor of the AOD pilot 1020 or AOA pilot 1030.

FIG. 12 illustrates a flow chart of a base station and user equipmentprocedure for determining CSI values in MMB according to embodiments ofthe present disclosure. The embodiment of the process shown in FIG. 12is for illustration only. While the flow chart depicts a series ofsequential steps, unless explicitly stated, no inference should be drawnfrom that sequence regarding specific order of performance, performanceof steps or portions thereof serially rather than concurrently or in anoverlapping manner, or performance of the steps depicted exclusivelywithout the occurrence of intervening or intermediate steps. The processdepicted in the example depicted is implemented by a transmitter chainin, for example, a mobile station.

In some embodiments, the base station specifies three frequencies, andthese can be repetitions of the three tiered pilots at 1210. For each ofthese we may have a beginning and a period (b₁, f₁, t₁), (b₂, f₂, t₂)and (b₃, f₃, t₃) respectively. Further, for the pilot in each tier,there can be three stage parameters (k, l, m) as described above. In abaseline embodiment the base station transmits all these parameters at1210. These parameters can be put in a broadcast message which can beeither put in the PDCCH, PDSCH or PBCH. The UE then uses the values of(b_(i), f_(i), t_(i)) and (k_(i), l_(i), m_(i)) to recover CSI at 1220.The UE would then feed back the CSI at 1230.

FIG. 13 illustrates a flow chart of a base station and user equipmentprocedure for determining CSI values in MMB according to embodiments ofthe present disclosure. The embodiment of the process shown in FIG. 13is for illustration only. While the flow chart depicts a series ofsequential steps, unless explicitly stated, no inference should be drawnfrom that sequence regarding specific order of performance, performanceof steps or portions thereof serially rather than concurrently or in anoverlapping manner, or performance of the steps depicted exclusivelywithout the occurrence of intervening or intermediate steps. The processdepicted in the example depicted is implemented by a transmitter chainin, for example, a mobile station.

In some embodiments, the base station may specify a small list ofparameters in the cell which is then used to deduce the quantities (b,f, t) by the mobile stations. For example it could specify a parameter Pwhich is an upper bound on the number of paths in the channel and aparameter S, which is a proxy for the selectivity of the channel, at1310. These two parameters then determine the values of (k, l, m) foreach of the pilots and how frequently do the pilots repeat in frequencyat 1320. For example there could be three levels of the parameters P andS, and the base station just needs to send 2 bits each to convey theselevels.

In some embodiments, the CSI pilot is chosen so that the required analogbeamforming at Tx and Rx coincide in time. This pilot structure ensuresthat the same RF chain can be used to form the desired beam (because abeam is fixed from one RF chain in one OFDM symbol).

FIG. 14 illustrates a flow chart of a base station and user equipmentprocedure for determining CSI values in MMB according to embodiments ofthe present disclosure. The embodiment of the process shown in FIG. 14is for illustration only. While the flow chart depicts a series ofsequential steps, unless explicitly stated, no inference should be drawnfrom that sequence regarding specific order of performance, performanceof steps or portions thereof serially rather than concurrently or in anoverlapping manner, or performance of the steps depicted exclusivelywithout the occurrence of intervening or intermediate steps. The processdepicted in the example depicted is implemented by a transmitter chainin, for example, a mobile station.

Referring to FIG. 14, in some embodiments, the beginning point of eachpilot may be the same. Let the repetition period of the CQI pilot beequal to (f_(CQI), t_(CQI)), then the repetition period (f_(AOA),t_(AOA)) may be a multiple of the CQI pilot and the repetition period ofthe AOD pilot (f_(AOD), t_(AOD)) may be a multiple of the AOA pilot.With the understanding that whenever the AOA pilot occurs the CQI pilotis not present and whenever the AOD pilot occurs the AOA pilot is notpresent, or in other words the pilots puncture each other. Themultipliers can be denoted as r₁ and r₂. So, in this method, the BSBroadcasts (r₁, r₂) at 1410. The UE uses values r₁ and r₂ to deduce(b_(i), f_(i), t_(i)) at 1420, since the beginning point of each pilotmay be the same. The UE then feeds back CSI values at 1430.

In some embodiments, the AOA/AOD pilots can be removed if an open loopregion is allocated by the base station. In this open loop region thebase station transmits data to certain users in a spatial diversity modeby cycling through various Tx beams. The cycling pattern is known by allthe users in the system. Even through the user is not aware of the databeing sent or the CQI of each path, it can still deduce the AOA/AOD fromthis open loop region using a method such as Music of Esprint.

In some embodiments, the AOA/AOD can be deduced from other channels, forexample the PSS/SSS, or CRS. In this case, the pilot can be skipped.

In MMB large numbers of antennas can be used at the base station andmobile station. To estimate the channel it is necessary to isolate thecomponents that are slowly varying vs. those which are rapidly varying.This ensures that minimal pilot overhead is used in channel estimation.The disclosed embodiments provide several ways to accomplish this.

FIG. 15 illustrates a wireless network 1500 according to one embodimentof the present disclosure. The embodiment of wireless network 1500illustrated in FIG. 15 is for illustration only. Other embodiments ofwireless network 1500 could be used without departing from the scope ofthis disclosure.

The wireless network 1500 includes eNodeB (eNB) 1501, eNB 1502, and eNB1503. The eNB 1501 communicates with eNB 1502 and eNB 1503. The eNB 1501also communicates with Internet protocol (IP) network 1530, such as theInternet, a proprietary IP network, or other data network.

Depending on the network type, other well-known terms may be usedinstead of “eNodeB,” such as “base station” or “access point”. For thesake of convenience, the term “eNodeB” shall be used herein to refer tothe network infrastructure components that provide wireless access toremote terminals. In addition, the term user equipment (UE) is usedherein to refer to remote terminals that can be used by a consumer toaccess services via the wireless communications network. Otherwell-known terms for the remote terminals include “mobile stations” and“subscriber stations.”

The eNB 1502 provides wireless broadband access to network 1530 to afirst plurality of user equipments (UEs) within coverage area 1520 ofeNB 1502. The first plurality of UEs includes UE 1511, which may belocated in a small business; UE 1512, which may be located in anenterprise; UE 1513, which may be located in a WiFi hotspot; UE 1514,which may be located in a first residence; UE 1515, which may be locatedin a second residence; and UE 1516, which may be a mobile device, suchas a cell phone, a wireless laptop, a wireless PDA, or the like. UEs1511-1516 may be any wireless communication device, such as, but notlimited to, a mobile phone, mobile PDA and any mobile station (MS).

For the sake of convenience, the term “user equipment” or “UE” is usedherein to designate any remote wireless equipment that wirelesslyaccesses an eNB, whether the UE is a mobile device (e.g., cell phone) oris normally considered a stationary device (e.g., desktop personalcomputer, vending machine, etc.). In other systems, other well-knownterms may be used instead of “user equipment”, such as “mobile station”(MS), “subscriber station” (SS), “remote terminal” (RT), “wirelessterminal” (WT), and the like.

The eNB 1503 provides wireless broadband access to a second plurality ofUEs within coverage area 1525 of eNB 1503. The second plurality of UEsincludes UE 1515 and UE 1516. In some embodiments, one or more of eNBs1501-1503 can communicate with each other and with UEs 1511-1516 usingLTE or LTE-A techniques including techniques for: using different pilotdesigns for millimeter wave broadband as described in embodiments of thepresent disclosure.

Dotted lines show the approximate extents of coverage areas 1520 and1525, which are shown as approximately circular for the purposes ofillustration and explanation only. It should be clearly understood thatthe coverage areas associated with base stations, for example, coverageareas 1520 and 1525, may have other shapes, including irregular shapes,depending upon the configuration of the base stations and variations inthe radio environment associated with natural and man-made obstructions.

Although FIG. 15 depicts one example of a wireless network 1500, variouschanges may be made to FIG. 15. For example, another type of datanetwork, such as a wired network, may be substituted for wirelessnetwork 1500. In a wired network, network terminals may replace eNBs1501-1503 and UEs 1511-1516. Wired connections may replace the wirelessconnections depicted in FIG. 1.

FIG. 16A is a high-level diagram of a wireless transmit path. FIG. 16Bis a high-level diagram of a wireless receive path. In FIGS. 16A and16B, the transmit path 1600 may be implemented, e.g., in eNB 1502 andthe receive path 1650 may be implemented, e.g., in a UE, such as UE 1516of FIG. 15. It will be understood, however, that the receive path 1650could be implemented in an eNB (e.g. eNB 1502 of FIG. 15) and thetransmit path 1600 could be implemented in a UE. In certain embodiments,transmit path 200 and receive path 1650 are configured to usingdifferent pilot designs for millimeter wave broadband as described inembodiments of the present disclosure.

Transmit path 1600 comprises channel coding and modulation block 1605,serial-to-parallel (S-to-P) block 1610, Size N Inverse Fast FourierTransform (IFFT) block 1615, parallel-to-serial (P-to-S) block 1620, addcyclic prefix block 1625, up-converter (UC) 1630. Receive path 1650comprises down-converter (DC) 1655, remove cyclic prefix block 1660,serial-to-parallel (S-to-P) block 1665, Size N Fast Fourier Transform(FFT) block 1670, parallel-to-serial (P-to-S) block 1675, channeldecoding and demodulation block 1680.

At least some of the components in FIGS. 16A and 16B may be implementedin software while other components may be implemented by configurablehardware (e.g., a processor) or a mixture of software and configurablehardware. In particular, it is noted that the FFT blocks and the IFFTblocks described in this disclosure document may be implemented asconfigurable software algorithms, where the value of Size N may bemodified according to the implementation.

Furthermore, although this disclosure is directed to an embodiment thatimplements the Fast Fourier Transform and the Inverse Fast FourierTransform, this is by way of illustration only and should not beconstrued to limit the scope of the disclosure. It will be appreciatedthat in an alternate embodiment of the disclosure, the Fast FourierTransform functions and the Inverse Fast Fourier Transform functions mayeasily be replaced by Discrete Fourier Transform (DFT) functions andInverse Discrete Fourier Transform (IDFT) functions, respectively. Itwill be appreciated that for DFT and IDFT functions, the value of the Nvariable may be any integer number (i.e., 1, 2, 3, 4, etc.), while forFFT and IFFT functions, the value of the N variable may be any integernumber that is a power of two (i.e., 1, 2, 4, 8, 16, etc.).

In transmit path 1600, channel coding and modulation block 1605 receivesa set of information bits, applies coding (e.g., LDPC coding) andmodulates (e.g., Quadrature Phase Shift Keying (QPSK) or QuadratureAmplitude Modulation (QAM)) the input bits to produce a sequence offrequency-domain modulation symbols. Serial-to-parallel block 1610converts (i.e., de-multiplexes) the serial modulated symbols to paralleldata to produce N parallel symbol streams where N is the IFFT/FFT sizeused in eNB 1502 and UE 1516. Size N IFFT block 1615 then performs anIFFT operation on the N parallel symbol streams to produce time-domainoutput signals. Parallel-to-serial block 1620 converts (i.e.,multiplexes) the parallel time-domain output symbols from Size N IFFTblock 1615 to produce a serial time-domain signal. Add cyclic prefixblock 1625 then inserts a cyclic prefix to the time-domain signal.Finally, up-converter 1630 modulates (i.e., up-converts) the output ofadd cyclic prefix block 1625 to RF frequency for transmission via awireless channel. The signal may also be filtered at baseband beforeconversion to RF frequency.

The transmitted RF signal arrives at UE 116 after passing through thewireless channel and reverse operations to those at eNB 1502 areperformed. Down-converter 1655 down-converts the received signal tobaseband frequency and remove cyclic prefix block 1660 removes thecyclic prefix to produce the serial time-domain baseband signal.Serial-to-parallel block 1665 converts the time-domain baseband signalto parallel time domain signals. Size N FFT block 1670 then performs anFFT algorithm to produce N parallel frequency-domain signals.Parallel-to-serial block 1675 converts the parallel frequency-domainsignals to a sequence of modulated data symbols. Channel decoding anddemodulation block 1680 demodulates and then decodes the modulatedsymbols to recover the original input data stream.

Each of eNBs 1501-1503 may implement a transmit path that is analogousto transmitting in the downlink to UEs 1511-1516 and may implement areceive path that is analogous to receiving in the uplink from UEs1511-1516. Similarly, each one of UEs 1511-1516 may implement a transmitpath corresponding to the architecture for transmitting in the uplink toeNBs 1501-1503 and may implement a receive path corresponding to thearchitecture for receiving in the downlink from eNBs 1501-1503.

FIG. 17 illustrates a subscriber station according to embodiments of thepresent disclosure. The embodiment of subscribe station, such as UE1516, illustrated in FIG. 17 is for illustration only. Other embodimentsof the wireless subscriber station could be used without departing fromthe scope of this disclosure.

UE 1516 comprises antenna 1705, radio frequency (RF) transceiver 1710,transmit (TX) processing circuitry 1715, microphone 1720, and receive(RX) processing circuitry 1725. SS 116 also comprises speaker 1730, mainprocessor 1740, input/output (I/O) interface (IF) 1745, keypad 1750,display 1755, and memory 1760. Memory 1760 further comprises basicoperating system (OS) program 1761 and a plurality of applications 1762.The plurality of applications can include one or more of resourcemapping tables (Tables 1-10 described in further detail herein below).

Radio frequency (RF) transceiver 1710 receives from antenna 1705 anincoming RF signal transmitted by a base station of wireless network1500. Radio frequency (RF) transceiver 1710 down-converts the incomingRF signal to produce an intermediate frequency (IF) or a basebandsignal. The IF or baseband signal is sent to receiver (RX) processingcircuitry 1725 that produces a processed baseband signal by filtering,decoding, and/or digitizing the baseband or IF signal. Receiver (RX)processing circuitry 1725 transmits the processed baseband signal tospeaker 1730 (i.e., voice data) or to main processor 1740 for furtherprocessing (e.g., web browsing).

Transmitter (TX) processing circuitry 1715 receives analog or digitalvoice data from microphone 1720 or other outgoing baseband data (e.g.,web data, e-mail, interactive video game data) from main processor 1740.Transmitter (TX) processing circuitry 1715 encodes, multiplexes, and/ordigitizes the outgoing baseband data to produce a processed baseband orIF signal. Radio frequency (RF) transceiver 1710 receives the outgoingprocessed baseband or IF signal from transmitter (TX) processingcircuitry 1715. Radio frequency (RF) transceiver 1710 up-converts thebaseband or IF signal to a radio frequency (RF) signal that istransmitted via antenna 1705.

In certain embodiments, main processor 1740 is a microprocessor ormicrocontroller. Memory 1760 is coupled to main processor 1740.According to some embodiments of the present disclosure, part of memory1760 comprises a random access memory (RAM) and another part of memory1760 comprises a Flash memory, which acts as a read-only memory (ROM).

Main processor 1740 executes basic operating system (OS) program 1761stored in memory 1760 in order to control the overall operation ofwireless subscriber station 1516. In one such operation, main processor1740 controls the reception of forward channel signals and thetransmission of reverse channel signals by radio frequency (RF)transceiver 1710, receiver (RX) processing circuitry 1725, andtransmitter (TX) processing circuitry 1715, in accordance withwell-known principles.

Main processor 1740 is capable of executing other processes and programsresident in memory 1760, such as operations for determining a newlocation for one or more of a DMRS or PSS/SSS as described inembodiments of the present disclosure. Main processor 1740 can move datainto or out of memory 1760, as required by an executing process. In someembodiments, the main processor 1740 is configured to execute aplurality of applications 1762, such as applications for using differentpilot designs for millimeter wave broadband. The main processor 1740 canoperate the plurality of applications 1762 based on OS program 1761 orin response to a signal received from BS 1502. Main processor 1740 isalso coupled to I/O interface 1745. I/O interface 1745 providessubscriber station 1516 with the ability to connect to other devicessuch as laptop computers and handheld computers. I/O interface 1745 isthe communication path between these accessories and main controller1740.

Main processor 1740 is also coupled to keypad 1750 and display unit1755. The operator of subscriber station 1516 uses keypad 1750 to enterdata into subscriber station 1516. Display 1755 may be a liquid crystaldisplay capable of rendering text and/or at least limited graphics fromweb sites. Alternate embodiments may use other types of displays.

Although the present disclosure has been described with an exemplaryembodiment, various changes and modifications may be suggested to oneskilled in the art. It is intended that the present disclosure encompasssuch changes and modifications as fall within the scope of the appendedclaims.

What is claimed is:
 1. A transmitter in a wireless network configuredto: utilize a pilot design and channel estimation strategy to reducepilot overhead, the pilot design based on a channel decomposition of thechannel in a ray tracing channel model.
 2. The transmitter of claim 1,further configured to: assign a first tier pilot to a first set ofresource blocks; assign a second tier pilot to second set of resourceblocks; assign a third tier pilot in a third set of resource blocks,wherein when two of the pilots are assigned to a common resource block,the lower tier pilot is given preference over the higher tier pilot; andtransmit each of the first tier pilot, the second tier pilot, and thethird tier pilot to a user equipment.
 3. The transmitter of claim 1,further configured to broadcast from a base station information relatingto the pilot structure.
 4. The transmitter of claim 3, furtherconfigured to broadcast a repetition value of a pilot in time andfrequency.
 5. The transmitter of claim 1, wherein the channeldecomposition is based on: $H = {{\begin{bmatrix}1 & 1 & \ldots & 1 \\^{j\; \theta_{1}} & ^{j\; \theta_{2}} & \ldots & ^{j\; \theta_{p}} \\\vdots & \vdots & \vdots & \vdots \\^{{({n_{R} - 1})}j\; \theta_{1}} & ^{{({n_{R} - 1})}j\; \theta_{2}} & \ldots & ^{{({n_{R} - 1})}j\; \theta_{P}}\end{bmatrix}\begin{bmatrix}h_{1} & 0 & \ldots & 0 \\0 & h_{2} & \ldots & 0 \\\vdots & \vdots & \vdots & \vdots \\0 & 0 & \ldots & h_{p}\end{bmatrix}}{\quad\begin{bmatrix}1 & ^{j\; \theta_{1}} & \ldots & ^{{({n_{t} - 1})}j\; \theta_{1}} \\1 & ^{j\; \theta_{2}} & \ldots & ^{{({n_{t} - 1})}j\; \theta_{2}} \\\vdots & \vdots & \vdots & \vdots \\1 & ^{j\; \theta_{p}} & \ldots & ^{{({n_{t} - 1})}j\; \theta_{p}}\end{bmatrix}}}$
 6. A wireless network configured to: transmit pilotsignals in a resource block using a plurality of antennas, wherein thenumber of pilot signals in the resource block is less than a number ofantennas used to transmit the pilot signals in the resource block. 7.The wireless network of claim 6, further configured to: assign a firsttier pilot to a first set of resource blocks; assign a second tier pilotto second set of resource blocks; assign a third tier pilot in a thirdset of resource blocks, wherein when two of the pilots are assigned to acommon resource block, the lower tier pilot is given preference over thehigher tier pilot; and transmit each of the first tier pilot, the secondtier pilot, and the third tier pilot to a user equipment.
 8. Thewireless network of claim 6, further configured to: broadcast, from abase station, information relating to the pilot structure, receiving theinformation at the user equipment; determine the pilot structure withthe information broadcast from the base station; and return CSI valuesfrom the user equipment to the base station.
 9. A method of using athree tiered pilot design in a millimeter wave broadband (MMB) wirelessnetwork to estimate channel state information (CSI), comprising:assigning a first tier pilot to a first set of resource blocks;assigning a second tier pilot to second set of resource blocks;assigning a third tier pilot in a third set of resource blocks, whereinwhen two of the pilots are assigned to a common resource block, thelower tier pilot is given preference over the higher tier pilot; andtransmitting each of the first tier pilot, the second tier pilot, andthe third tier pilot to a user equipment.
 10. The method according toclaim 9, wherein the first tier pilot is an angle of departure (AOD)pilot, the second tier pilot is an angle of arrival (AOA) pilot, and thethird tier pilot is a CSI pilot.
 11. The method according to claim 9,wherein at least one pilot is assigned to each resource block.
 12. Themethod according to claim 9, wherein each pilot tier is assigned with agiven starting resource block, and a given interval between pilots. 13.A method of establishing a pilot structure between a base station and aUE, comprising: broadcasting from the base station information relatingto the pilot structure; receiving the information at the user equipment;determining the pilot structure with the information broadcast from thebase station; and returning CSI values from the user equipment to thebase station.
 14. The method according to claim 13, wherein broadcastingfrom the base station includes broadcasting a number of RF chains usedfor a pilot, and further wherein determining the pilot structureincludes using the value of the number of RF chains to deduce a basestation precoder hopping pattern.
 15. The method according to claim 13,wherein broadcasting from the base station includes broadcasting asingle parameter P, and further wherein determining the pilot structureincludes decoding at least three parameters from P.
 16. The methodaccording to claim 13, wherein broadcasting from the base stationincludes broadcasting a repetition of a pilot in time and frequency, andwherein determining the pilot structure includes using the values of therepetition of a pilot in time and frequency to locate a CSI pilot anddetermine a receiver beamforming strategy.
 17. The method according toclaim 13, wherein broadcasting from the base station includesbroadcasting a plurality of parameters for a plurality of tiers ofpilots.
 18. The method according to claim 13, wherein broadcasting fromthe base station includes broadcasting a plurality of parameters for aplurality of tiers of pilots.
 19. The method according to claim 13,wherein broadcasting from the base station includes broadcasting twoparameters for a plurality of tiers of pilots, and wherein determiningthe pilot structure includes using the two parameters to deduce a pilotstructure for the plurality of tiers of pilots.
 20. The method accordingto claim 13, wherein the plurality of tiers of pilots includes a pilotfor determining an angle of arrival pilot, an angle of departure pilot,and a channel state information pilot.